真正陆生的变温、羊膜动物

1. 真正陆生的变温、羊膜动物 －爬行纲（Reptilia）

2. THE REPTILES PHYLUM CHORDATA CLASS REPTILIA • Repti1es are the first truly terrestrial vertebrates. • With some 6,000 species (about 300 species in the United States and Canada) occupying a great variety of aquatic and terrestrial habitats, they are clear1y a successful group. Nevertheless, repti1es are perhaps remembered best for what they once were, rather than for what they presently are. The Age of Dinosaurs(恐龙), which lasted 100 mi1lion years encompassing the Jurassic（侏罗纪） and Cretaceous（白垩纪） periods, saw the appearance of a great radiation of reptiles, many of huge stature（身材） and awesome（可怕） appearance, that completely dominated（支配） life on land. Then they suddenly declined（灭绝）. Out of the dozen or so principal groups of repti1es that evolved, four remain today. The most successful of these are the lizards（蜥蜴） and snakes of the order Squamata（有鳞目）. A second group is the crocodi1ians（鳄鱼）: having survived for 200 million years, they may finally be made extinct by man. To a third group belong the tortoises and turtles of the order Testudines（龟鳖目）, an ancient group that has somehow survived and remained mostly unchanged from its early repti1e ancestors. The last group is a relic stock represented today by a sole survivor, the tuatara（大蜥蜴） of New Zealand.

3. Reptiles are easily distinguished from amphibians by their scaly hide（皮）, which resists desiccation(干燥). But more than any other sing1e aspect, reptiles are set apart from amphibians by their method of reproduction. Reptiles lay eggs on land: amphibians must lay their eggs in water. This seemingly simple difference was in fact a remarkab1e evolutionary achievement that was to have a profound impact（效果） on subsequent vertebrate evolution. As we have seen, the amphibians are basica1ly aquatic animals by virtue of their reproduction. To totally abandon（遗弃） an aquatic life, there evolved a sophisticated interna11y-ferti1ized egg containing a comp1ete set of life-support systems. • This amniotic egg （羊膜卵）could be laid on dry land. Within, the embryo floats and develops in an aquatic environment surrounded by a membrane (the amnion): it is provided with a yolk sac containing its food supply; another membrane serves as a surface for gas exchange through the shel1: and provision is made for storing waste products that accumulate（堆积） during development . The early reptiles that deve1oped this egg would certainly have enjoyed an immediate advantage over the amphibians. They could now hide their vulnerable eggs in a protected situation away from water--and away from the numerous creatures that fed freely on the eggs provided by amphibians each spring. With the evolution of this ultimate adaptation, conquest of 1and by the vertebrates was now possib1e.

4. 爬行纲是体被角质鳞或硬甲、在陆地繁殖的变温羊膜动物（Amniota）。是一支从古两栖类在古生代石炭纪末期分化出来产羊膜卵的类群，它们不但继承了两栖动物初步登陆的特性，而且在防止体内水分蒸发，以及适应陆地生活和繁殖等方面，获得了进一步发展。爬行类是真正的陆栖脊椎动物，同时古爬行类还是鸟、兽等更高等的恒温羊膜动物的演化原祖，因此，本纲动物在脊椎动物进化中具有承上启下、继往开来的重要意义。 • 爬行动物为真正脱离水环境的陆地生活（有些现代种类为水中生活，属于次生性现象）的类群。同两栖动物比较，需要解决以下几个问题： • （1）陆地繁殖的问题 • （2）防止体内水分蒸发(丢失) • （3）陆地长距离运动，适应辐射

5. Characteristics • 1. Body variab1e in shape, compact in some, elongated in others, body covered with an exoskeleton of horny epidermal scales with the addition sometimes of bony dermal plates: integument with few glands • 2. Limbs paired, usually with five toes, and adapted for climbing, running, and paddling（划浆）, absent in snakes • 3. Ske1eton well ossified; ribs with sternum（胸骨） forming a complete thoracic basket: skull with one occipital condyle（枕髁） • 4. Respiration by lungs; no gills; cloaca（泄殖腔） used for respiration by some, branchial arches in embryonic life • 5. Three-chambered heart; crocodiles（鳄鱼） with four chambered heart; usually one pair of aortic arches • 6. Kidney a metanephros (paired)（后肾）; uric acid main nitrogenous waste • 7. Nervous system with the optic 1obes （视叶）on the dorsal side of brain: 12 pairs of cranial nerves in addition to nervus terminalis • 8. Sexes separate; fertilization internal • 9. Amniotic eggs, which are covered with leathery（坚韧的） shells; extra embryonic membranes including the amnion, chorion（绒毛膜）, yolk sac, and allantois（尿囊） present during embryonic 1ife brief classification

6. 特征 体表被角质鳞或骨板，缺少皮肤腺； 具典型五指（趾）型四肢，指端具爪； 头骨有颞窝，出现完整或不完整的次生腭；荐椎和颈椎数目增多，胸廓出现； 以肺呼吸； 心室出现不完全分隔，仍为不完全双循环； 出现新脑皮，脑神经为12对； 鼓膜下陷形成外耳道； 后肾为排泄器官，排泄物以尿酸为主； 体内受精，具羊膜卵； 变温。

7. 进一步适应陆生和进化的特征 1 表皮角质层的分化，缺少皮肤腺。 2 骨骼的进一步分化： 头骨：颞窝、单枕髁 脊柱：颈椎，胸椎，腰椎，荐椎， 尾椎 3 胸廓出现： 4 排泄方式（后肾）和排泄物（尿酸） 5 体内受精 6 脑神经12对，出现新脑皮。

9. 1 羊膜卵（amniotic egg）出现

11. 羊膜： 在胚胎发育形成原肠后，胚胎周围的表层胚膜向下二个方向发生皱折，这种皱折不断扩大，向上的皱折从底部包上去，最后两侧边缘打通，内层包住胚胎形成羊膜。 羊膜腔： 羊膜围住的腔为羊膜腔，里面充满羊水，胚胎悬浮羊水中。 绒毛膜：向上折叠的外层胚膜成为绒毛膜（浆膜） 尿 囊：在胚胎消化的后端形成的囊状突起，的胚胎的排泄和呼吸器官。 卵黄囊：胚膜的向下折叠押通后内层形成卵黄囊，包住卵黄。

12. 羊膜卵的出现在动物进化上的意义 1）羊膜卵可以产在陆地上并在陆地孵化。 2）体内受精，受精可无需借助水作为介质。 3）胚胎悬浮在羊水中，使胚胎在自身的“水域中”发育，环境更稳定，既避免了陆地干燥的威胁，又减少振动，以防机械损伤。 小结： 羊膜卵的出现是脊椎动物演化史上的一个飞跃。 羊膜卵的出现解除了脊椎动物个体发育中对水的依赖，使脊椎动物完全陆生成为可能，使陆生脊椎动物能向陆地的各种不同栖息环境发展也成为可能。

13. 爬行纲的身体结构特征 爬行动物是身披骨质鳞片，在陆地上繁殖的变温动物 .1 体形多样化 爬行动物躯体分成五部分：头、颈、躯干、四肢和尾 为适应不同的生活环境，爬行动物的体形向多样化发展 可分成三种类型： 龟鳖型：五部分化明显，躯体扁平，尾长短于体长 蜥蜴型：五部分化明显，尾长长于体长 蛇 型：五部分化不明显，四肢退化，尾长短于体长

14. 2 皮肤干燥，具角质鳞 • 皮肤由多层的表皮和真皮组成。树栖种类：棱鳞；鳄：角质鳞+真皮骨板；龟：角质盾+真皮骨板 • 表皮高度角质化，在表面产生角质鳞片，防止水分蒸发。 • 皮肤干燥，皮肤腺极少。股腺： • 蜕皮

18. skeleton • The skeleton of the early reptiles (cotylosaurs) （杯龙）was simi1ar to that of the labyrinthodont（迷齿类） amphibians. Most changes in later reptiles involved a loss of skul1 elements (by fusion or otherwise) and adaptable transformations for better locomotion. The nostrils of an al1igator or crocodi1e are on the dorsal side of the head and the internal nares are at the back of the throat, which can be closed on by a fold. Thus the reptile can breathe while holding its prey submerged. The reptilian skull has developed a more flexible joint with the vertebral column, and more efficient girdles were evolved for supporting the body. • The toes are provided with claws. Their peg1ike（钉子状） teeth vary somewhat but do not show the differentiation of the mammal; they may be set in sockets (thecodont) （槽生齿 ）or fused to the surface of the bone (acrodont)（颌缘）. • In many the teeth are formed in two rows along the edges of the premaxi1lae and maxillae, in the upper jaw, and along the dentaries（有齿的） of the lower jaw. Teeth may also be present on some of the palate bones. They are absent in turtles, in which only a horny beak is present.

19. 3 骨骼支持和肌肉系统 （1）四肢骨结构和运动特点 • 具有典型的五趾（指）型四肢 • 四肢骨与中轴骨呈横向直角关系，不能将身体抬离地面，运动时以爬行为主要方式

20. （2）头骨特点 • 具颞窝 无颞窝类：无颞窝。古杯龙类属。传统分类观点认为现代龟鳖类头骨属无颞窝类，但有些种类出现次生性孔洞。 双颞窝类：头骨每侧有2个颞窝，大多数古代爬行类、大多数现代爬行类(蜥蜴、蛇、鳄)和鸟类属于此类。 合颞窝类：头骨每侧有1个颞窝，古代兽齿类和由此演化出的哺乳类属于此类。

21. 出现次生腭 次生腭使口腔和鼻腔分隔，内鼻孔后移，使呼吸通畅，效率提高，在吞食大型食物时可正常呼吸。 鳄类有完整的次生腭，鼻腔和口腔完全分隔。 • 单枕髁

23. （3）脊柱进一步分化 颈椎、胸椎、腰椎、荐椎、尾椎 椎体：低等双凹型，其余后凹或前凹； 颈椎：数目加多，第一为环椎、第二为枢椎， 颈椎数目不定。环椎孔被一韧带为上下两部，上部通过脊髓，下部容纳齿突。 荐椎：2块，加强、承重，横突发达，通过腰带关节使后肢承受体重的机能加强。

24. （4）出现胸廓：胸椎、肋骨、胸骨围成，保护内脏，增强了肺呼吸。（4）出现胸廓：胸椎、肋骨、胸骨围成，保护内脏，增强了肺呼吸。 • （5）肩带与两栖基本相同，腰带（两栖：坐骨、耻骨；爬行：髂骨、坐骨、耻骨）；腰带骨间出现孔洞。耻骨和坐骨之间出现耻坐孔，减轻腰带重量，不影响承重能力。

25. （6）肌肉系统：躯干肌复杂化，肋间肌和皮肤肌出现。肋间肌（包括肋间外肌和肋间内肌）的运动牵引肋骨改变胸廓容积以完成呼吸动作。皮肤肌连接角质鳞片，其收缩可牵引鳞片辅助爬行，蛇类尤其发达。（6）肌肉系统：躯干肌复杂化，肋间肌和皮肤肌出现。肋间肌（包括肋间外肌和肋间内肌）的运动牵引肋骨改变胸廓容积以完成呼吸动作。皮肤肌连接角质鳞片，其收缩可牵引鳞片辅助爬行，蛇类尤其发达。

26. 骨骼 1）骨化程度较高，硬骨比重大，趾端具爪，适于爬行。 2）脊椎骨分化为陆生脊椎动物典型的五个区域： 颈椎、胸椎、腰椎、荐椎、尾椎 躯椎分化为胸椎和腰椎，颈椎数目增多，荐椎增至 2枚，第1、2节颈椎特化为寰椎和枢椎，与枕髁形成 可动联接

27. 3）头骨具单一枕髁，有颞窝形成 颞窝：为头颅两侧， 眼眶后面的凹陷，是咬肌着生的部位 作用：可增大咬肌附着面积，增强咀嚼能力。 4）开始具有胸廓 爬行动物在颈椎、胸椎和腰椎两侧都有肋骨，而胸椎的肋骨与胸骨形成胸廓，可保护内脏和加强呼吸作用。 胸廓是羊膜动物所特有 5）具次生颚，内鼻孔后移，口腔与鼻腔分开

28. Most reptiles are carnivorous and their digestive system is adapted for such a diet. All are provided with a tongue. This is large, fleshy（肉质的）, and broad in crocodiles and turtles. In crocodiles a tongue fold with a simi1ar fold of the palate（味觉） can separate the air passage from the food passage. In some repti1es (chameleon变色龙) the tongue is highly protrusible and is used in catching their prey. When not in use, the anterior part of such a tongue is telescoped into the posterior portion. Buccal（颊） g1ands vary a great deal. In snakes the upper labial（唇） glands may be modified into poison glands. The stomach is usual1y spind1e shaped and contains gastric glands. Pebbles（小圆石） or gastroliths（胃石） are found in some reptiles (crocodiles) for grinding（研磨） the food. A short duodenum（十二指肠） receives the ducts from the liver and pancreas（胰腺）. The walls of the midgut are thrown into folds, but there are few g1ands. The cloaca (Fig. 24-2), which receives the rectum（直肠）, ureters（输尿管）, and reproductive ducts, may be complicated. A urinary bladder is found in shenodon. turtles, and most lizards and opens into the ventra1 wall of the cloaca（泄殖腔）

29. 消化系统：消化道进一步复杂化 1）具齿：多为同型齿 从爬行动物开始出现的牙齿，是重要的消化器官 脊椎动物的牙齿根椐其着生部位可分3 种类型： 端生齿：着生在颌骨的端面，是最原始的类型。 侧生齿：着生在颌骨的边缘内侧，如蜥蜴和蛇 槽生齿：着生在颌骨上的齿槽内，最为牢固 2）具发达的口腔腺，口腔腺能润湿食物，帮助吞咽。 毒蛇的口腔腺特化为毒腺 3）大、小肠交界处开始出现盲肠， 与纤维素消化有关

31. All reptiles have lungs for breathing. The glottis（声门） behind the tongue is c1osed by special musc1es. The larynx contains arytenoid（勺状软骨） and cricoid cartilages but no thyroid（甲状软骨） cartilages. The trachea（气管） is provided with semicircular cartilage rings to keep it open. Lungs are mainly simple sacs in sphenodon and snakes (in which one is reduced), but in turtles and crocodiles they are divided into irregular chambers（不规则的室）, with the alveoli（气泡） connected to branched series of bronchial tubes（支气管）. In chameleons（变色龙） 1ong, ho1low processes of the lungs pass posteriorly among the viscera and represent forerunners（先驱） of the air sacs of birds. Air is drawn into the lungs by the movements of the ribs and, in crocodiles, by the muscular diaphragm（隔膜）.

32. 5 肺呼吸进一步完善 肺内壁具有较两栖类复杂的分隔，与空气交换面积扩大；口腔和呼吸道由于次生腭出现而明显分开；气管和支气管明显分化；声带较为简单，一般不发声。 蛇和蛇蜥左肺萎缩 靠胸廓的扩张和缩小，使肺内和呼吸道中的气压与外界大气压产生差别，而将气体吸入或排出。 蝮蛇和避役肺前部为呼吸部,后部为气囊.

33. 1）肺呈海绵状，有气管、支气管 2）进行咽式呼吸和胸式呼吸 3）次生性水生种类在咽和泄殖腔壁上都有丰富的毛细血管，可进行辅助呼吸。

35. Since there is no branchial circulation in reptiles, on each side the fifth aortic arch is lost, the third becomes the carotid arch（颈动脉弓）, the fourth the systemic arch（主动脉弓）, and the sixth the pulmonary arteries（肺动脉）. The systemic arches are paired, in contrast to the sing1e one of birds and mammals. In crocodiles there are two completely separated ventric1es: in the other groups the ventricle is incomp1ete1y separated. Crocodiles are thus the first animals with a four-chambered heart . The conus and truncus arteriosus are absent. Venous blood is returned to the sinus venosus（静脉窦） of the heart through the paired precaval（前腔） and the sing1e postcaval veins. Rena1 and hepatic portal systems are present. The blood contains oval, nuc1eated corpuscles that are smaller than those of amphibians.

36. 6 血液循环仍为不完全双循环 • 心脏： 2心房和1心室，心室出现不完全分隔，鳄类心室室分隔只留有一孔。多氧血和缺氧血仍不能完全分开。 • 动脉和静脉：动脉圆锥消失，静脉窦退化。三对动脉弓的直径和位置不同. • 通入头部的颈总动脉由右体动脉弓发出 • 静脉系统类似两栖动物

41. The excretory system is made up of the paired elongated or compact kidneys (metanephroi), composed of glomerular nephrons. Ureters carry the urine (fluid in turtles and crocodiles: semisolid with insoluble urates in the others) to the cloaca.

42. 7 具有羊膜动物式的排泄器官----后肾 后肾完全失去体腔联系，以血管收集废物，后肾管输尿。 排泄产物为尿酸。爬行类中的蜥蜴和龟鳖类具有尿囊基部扩大形成的膀胱，在干旱地区的种类膀胱具有吸收水分的功能。许多种类在鼻部或眼部附近具有盐腺，能排出浓度很高的盐溶液。盐腺的重量甚至超过肾脏

44. The male reproductive system consists of paired elongated testes that are connected to the vasa deferentia (the wolf fan or mesonephric ducts) . The latter carry sperm to the copulatory organ（交配器官）, which is an evagination（外翻） of the cloacal（泄殖腔） wall and is used for internal fertilization. These copulatory organs are single in crocodiles and turtles but paired in lizards and snakes, in which they are called hemipenes（半阴茎）. The female system is made up of large paired ovaries, and the eggs are carried to the cloaca by oviducts, which are provided with funnel-shaped ostia. The glandu1ar wal1s of the oviducts secrete albumin and shells for the large amniote eggs. The embryonic membranes (amnion, yolk sac, al1antois, and chorion), first appear in reptiles and are used for the nourishment, protection, and respiration of the embryo

45. 8 生殖 • 受精在母体内进行。 • 卵生（羊膜卵，少数卵胎生，将卵产于温暖潮湿、阳光充足的地方；或有营巢习性，如多数毒蛇和一些蜥蜴类）。 • 雄性均有交配器（楔齿蜥除外）。蛇与蜥蜴的交配器为半阴茎（泄殖腔壁突起形成）。龟鳖类和鳄类为一个阴茎，内有阴茎海绵体，属真正的交配器。

48. 可作为分类和探索亲缘关系的依据

49. The repti1ian nervous system shows many advancements over that of the amphibians. The cerebrum is en1arged, and there has been a transfer of some nervous integrative activities forward to the forebrain. Relatively, however, the brain is sma1l, never exceeding 1% of the body weight. There are 12 pairs of cranial nerves in addition to the nervous terminalis. A better developed peripheral nervous system is associated with the more efficient limbs of reptiles. Sense organs vary among the different reptilian groups, but in general they are well deve1oped.

50. The lateral-line system, however, is entirely 1ost. • The sense of hearing is poorly developed in most. • A1l repti1es have a middle and inner ear, and crocodiles have an outer one as well. The middle ear contains the ear ossic1e (stapes) and communicates with the pharynx by the eustachian（耳咽管） tube. Jacobson's organ, a unique sense organ, is a separate part of the nasal sac and communicates with the mouth; it is especial1y well developed in snakes and lizards. It is innervated by a branch of the olfactory nerve and is used in smel1ing the food in the mouth cavity. In snakes, environmental odors trapped on the flickering tongue are carried into the mouth and to Jacobson s organ. This organ in some form is found in other groups, including the amphibians.